1. Field of the Invention
The invention relates to a method for producing a boom arm having a boom-arm body and having at least one pipe holder for a concrete-distributing boom and to a concrete-distributing boom for stationary and mobile concrete pumps having a plurality of boom arms which are connected to one another such that they can be pivoted about an axis of articulation at folding articulations and retain a concrete-delivery line, which has at least one rotary articulation and which has an axis of rotation aligned with an axis of articulation of a folding articulation, wherein the at least one pipe holder has a pipe-carrier portion for accommodating the concrete-delivery line at a retaining location, of which the siting is predetermined by the position of the axis of articulation.
2. Description of the Related Art
A concrete-distributing boom of the type mentioned in the introduction is known from DE 196 44 410 A1. The concrete-distributing boom described therein contains a concrete-delivery line and has three boom arms which are connected via folding articulations and can be adjusted by a hydraulic transmission. The concrete-delivery line in the concrete-distributing boom is made up of a multiplicity of pipe segments, which are retained on the boom arms by pipe holders.
Concrete-distributing booms frequently have not just three, but four, five or even more boom arms. The length of the individual boom arms is usually between 6 m and 8 m. In order that a concrete-distributing boom can be extended an overall length of up to 60 m or more, the boom arms in a concrete-distributing boom have to meet very high stability-related requirements. The required stability can be achieved by boom-arm bodies which comprise welded structures with a box profile joined together from four steel sheets. The large dimensions of the steel sheets and the introduction of heat during thermal joining result in said boom-arm bodies having very large production tolerances. These production tolerances are considerably larger than those which are necessary to meet the accuracy-related requirements for arranging the articulations and for positioning the hydraulic transmissions for moving the boom arms in a concrete-distributing boom.
During the production of concrete-distributing booms, it is therefore necessary for the welded structures of the boom-arm bodies to be subjected to high-outlay mechanical follow-up machining. Such mechanical follow-up machining holds the risk of the material being weakened in specific portions of a boom-arm body. In order for the required stability not to be adversely affected, the mechanical follow-up machining for welded structures of boom-arm bodies is reduced to a minimum.
In order that the boom-arm bodies in a concrete-distributing boom are not subjected to unnecessary loading, it is important for the axes of rotation of the rotary articulations of the delivery line and the axes of articulation of the folding articulations in the concrete-distributing boom to correspond very precisely. This makes it necessary to compensate for production tolerances.
In order to compensate for production tolerances, the pipe holders for accommodating the concrete-delivery line are usually adapted individually to the boom-arm bodies in a concrete-distributing boom and then welded on. The weld connections here are produced by hand, the concrete-delivery line in the first instance being preassembled on a boom-arm body and a pipe holder, usually comprising a plurality of parts, then being roughly fixed, set in position and welded. These operating steps cannot be automated with justifiable outlay and therefore have to be carried out manually. The operating steps also require an installer to establish weld connections in awkward positions, which makes it very difficult, and involves high outlay, to maintain a required weld-seam quality. The individual adaptations which are necessary for the pipe holders therefore means that it is not just the installation of pipe holders on a boom arm which involves high outlay and is very expensive; this is also the case for exchanging pipe holders on a boom arm in the context of maintenance work.